1. Field of the Invention
This invention relates to a novel process for producing .alpha., .beta.-unsaturated aldehydes including industrial important fragrances such as citral and sinensal, starting materials for preparing pharmaceutical drugs such as senecioaldehyde, farnesal, and 8-acetoxy-2,6-dimethyl-2,6-octadienal, and the like.
Previously, there is generally known a process which comprises oxidizing allylic alcohols in the presence of an aluminum alkoxide catalyst to obtain the corresponding .alpha., .beta.-unsaturated aldehydes (refer to Organic Reactions, Vol. 6, Chapter 5, U.S. Pat. No. 4,663,488 (1987), and Japanese Patent Laid-open No. SHO 51 (1976)-141,801).
Also there is known a process which comprises reacting formic acid esters of secondary alcohols with cyclohexanone in large excess in the presence of aluminum alkoxide in a large amount under reflux by heating to obtain the corresponding ketones (refer to J. Am. Chem. Soc., Vol. 78, 816 (1956)).
2. Description of the Related Art
Formic acid esters of allylic alcohols can be readily prepared, for example, according to a process which comprises chlorination of double bond, or a process which comprises reacting sodium formate to allyl chlorides obtained by hydrochloric acid-addition reaction of a diene compound such as isoprene, myrcene, and the like (refer to Japanese Patent Laid-open No. SHO 63(1988)-227,546).
The process of preparing .alpha., .beta.-unsaturated aldehydes from formic acid esters of allylic alcohols comprises hydrolyzing the esters to the corresponding allylic type alcohols, and thereafter oxidizing the obtained allylic type alcohols. But this process has a long reaction sequence and therefore has been desired to be simplified.
Furthermore, the successful application of the well-known oxidizing process for formic acid esters in the presence of an aluminum alkoxide catalyst to prepare .alpha., .beta.-unsaturated aldehydes from formic acid esters of allylic type alcohols known as relatively high reactivity is difficult to obtain the objective .alpha., .beta.-unsaturated aldehydes in high yield because of the active side reactions including the self-condensation of produced .alpha., .beta.-unsaturated aldehydes etc. for its severe reaction conditions.
The object of the invention is to provide a process for producing .alpha., .beta.-unsaturated aldehydes, directly and in high yield, from readily available industrial starting materials such as formic acid esters of allylic type alcohols, dissolving the aforementioned problems.